The overall objective of our research is to develop a better understanding of transport across epithelial membranes. Substances transported across epithelial must cross at least two barriers in series, the membranes at the two sides of the cell layer and there is ample evidence indicating that these barriers have different functional properties. Studies are directed primarily toward obtaining information on the properties of these individual barriers in frog skin, mammalian intestine and toad colon and on understanding the way in which these barriers contribute to overall epithelial function. We hope to obtain much more detailed information on transport systems for sodium, amino acids and sugars located in the individual barriers and to develop a better understanding of molecular mechanisms involved. The mode of energy input and details of coupling between different transport process and between transport and metabolism is being examined.